1. Field of the Invention
The present invention relates to a method for discharging liquid, a method to discharge desired liquid by generating bubbles by applying thermal energy to liquid, liquid discharge head and liquid discharge device, and in particular relates to a method for discharging liquid using a movable member that is displaced by generation of bubbles.
In addition, the present invention is applicable to an apparatus such as a printer to execute recording on a recording medium to be recorded, such as paper, thread, fiber, fabric, leather, metal, plastic, glass, lumber, ceramics, a photocopier, a facsimile having transmission system, and a word processor having a printer part and the like and moreover to an industrial recording apparatus mixed in a complex fashion with various processing devices.
Incidentally, the term xe2x80x9crecordingxe2x80x9d in the present invention means not only to form images having intelligence such as letters and drawings etc. to a recording medium to be recorded but also means to form images not having intelligence such as patterns etc.
2. Related Background Art
Liquid jet recording method, or so-called bubble jet recording method, that gives energy such as heat to ink (liquid) to cause liquid to undergo status change accompanying precipitous volume change (generation of bubbles) and discharges liquid from a discharge port with application force based on this status change, causes the liquid to attach onto a recording medium to be recorded, and proceeds with image forming, is conventionally known. For a recording apparatus using this bubble jet recording method, as disclosed in the U.S. Pat. No. 4,723,129 publication etc., a discharge port to discharge liquid, a liquid flow path to communicate with this discharge port, and an electro-heat converter as energy generating means for discharging liquid disposed inside the liquid flow path are generally provided.
Such a recording method enables recording of high density images at a high speed and with low noise, and can dispose the discharge port to discharge liquid at a high density in the head to execute this recording method, and therefore has a lot of excellent advantages so as to easily obtain recorded images and moreover color images as well with high resolution with a small apparatus. Therefore, this bubble jet recording method has recently been utilized for a lot of office apparatus such as a printer, a photocopier and a facsimile etc. and moreover has become utilized even for systems for industrial use such as a textile printing apparatus etc.
A schematic section view around an electro-heat converter of liquid discharge head of a prior art example to execute recording by such a recording method is shown in FIG. 10. In the example shown in the above-described drawing, the electro-heat converter is constructed of a resistant layer 100 and electrodes 101a and 101b laminated thereon and formed as a pair having a gap. That is, the heat generating part 105 to generate heat by applying voltages is formed between the electrode 101a and the electrode 101b, and this part will become a bubble generation region where bubbles are formed by film boiling. In addition, above the resistant layer 100 and the electrodes 101a and 101b, two protection layers 102 and 103 protecting these are formed.
The discharge port to discharge liquid by generating a bubble 104 with heat generation at the heat-generating body 105 is disposed at a position facing the heat-generating body 105 such as the discharge port S (so-called side shooter type) or is disposed at the side direction such as the discharge port E (so-called edge shooter type). In any case, in the liquid discharge head with such construction, the bubble 104 grows comparatively large toward the liquid chamber side X with comparatively small flow path resistant, and therefore the bubble disappearance position 106 is likely to come to the center area of the heat-generating body 105 or a little bit biased to the direction of the liquid chamber side.
Thus, in the liquid discharge head as shown in FIG. 10, accompanied by growth of the bubble 104, the liquid is largely pushed back to the direction of the chamber side X. Accordingly, a meniscus, that is formed in the discharge port side, being the surface between the liquid and the outside atmosphere, retreats comparatively fast accompanied by bubble disappearance after liquid discharge, and vibrates comparatively long. In addition, in the bubble disappearance steps, a flow of liquid toward the heat-generating body 105 from the liquid chamber side and a flow of liquid toward the heat-generating body 105 from the discharge port reach approximately the same level, and thus the timing when refilling of liquid to the discharge port side substantially commences comes after the flow of liquid from the discharge port side approximately stops and proceeds comparatively late, and therefore it takes a comparatively long time until the meniscus comes back to the normal position to be stabilized. Thus, in the case where liquid is discharged in a consecutive fashion, it is necessary to take a time interval comparatively long for discharge and there is a limit for a drive frequency that can enable liquid to be discharged properly.
In addition, as a liquid discharge head, one is known that has a construction that includes a movable member provided in the bubble generating region to undergo displacement and accompanied by growth of bubbles and a controller to control the displacement of the movable member within a desired range. The controller faces the bubble generating region of the liquid flow path so that substantial contact between the movable member having undergone displacement and the controller constitutes a substantially closed space except the discharge port. In this liquid discharge head, at the time of growth of bubbles, displacement of the movable member takes place to substantially close the upper stream side flow path of the bubble generation region. The liquid to be pushed back to the upstream side at the time of growth of bubbles is comparatively small. In addition, at the time of bubble disappearance, the movable member undergoes displacement so as to make the flow resistance at the upstream side small, and bubble disappearance at the upstream side of the bubble generation region is promoted to occur ahead than at the downstream side. Therefore, the retreat quantity of the meniscus is small and refill of liquid is executed efficiently.
In addition, in the liquid discharge head, the gas having melted into the liquid is released at the time when bubbles are formed, giving rise to a case where microbubbles are formed and remain behind. Under this circumstance, so that a quantity of these microbubbles does not remain to cause trouble, the liquid in the vicinity of the discharge port is sucked out and a recovery operation such as removal of microbubbles is executed on a regular basis. On the other hand, in the liquid discharge head comprising the movable member, the liquid is never pushed back to the upstream side, and therefore the microbubbles are released from the discharge port before increasing in number enough to cause trouble in the discharge operation, and hardly remain behind. Therefore, over a comparatively long period, consecutive recording can be executed and, at maximum, it is possible to execute recording of 100 sheets or more in a consecutive manner.
As described above, the liquid discharge head including a movable member has an advantage that it can execute refilling of liquid swiftly without giving rise to considerable retreat of the meniscus, and therefore uses a comparatively short time interval. Discharge of liquid can be executed, and driving with a comparatively high frequency is possible.
In addition, conventionally, in order to arrange for driving at a higher frequency, it is considered to be practically effective to cause the bubbles formed due to the aforesaid discharge to undergo bubble disappearance fast to arrange to execute the next discharge. The reasons therefor are that in order to execute the next discharge properly, it is generally necessary to execute the next discharge after the meniscus comes back to the normal position via vibration steps to complete refilling stably, and that the completion of this refilling and the recovery and stability of the meniscus occurs at the end of bubble disappearance.
However, in order to complete bubble disappearance, a constant time period is theoretically required as well, and this time period will end to provide a limit to the driving interval. That is, in applying voltage pulses with several xcexcS widths in order to execute liquid discharge, the period for the bubble generation, their growth and disappearance can be made to be 30 to 50 xcexcS from the commencement of the pulse application is consideration of delay in response. Under these circumstances, even if the next pulse has been applied immediately after bubble disappearance to execute next discharge, the driving frequency is limited to 20 to 30 kHz. Under the circumstances, the present inventors thought that there would be no progress in technology without breaking through such a situation.
That is, an objective of the present invention is to break through the limit of the prior art related to execution of liquid discharge at higher frequency, and the present invention proposes a novel method for discharging liquid that can discharge liquid in a continuous fashion at a higher frequency.
A method for discharging liquid according to the present invention is a method for discharging liquid, in which a plurality of discharged liquid droplets are discharged from a same discharge port using a liquid discharge head. The liquid discharge head includes: a heat-generating body to generate thermal energy for generating bubbles in a liquid; a discharge port as a part to discharge the liquid; a liquid flow path communicating with the discharge port and having a bubble generation region to generate bubbles in the liquid; a liquid chamber to supply the liquid flow path with the liquid; a movable member provided in the bubble generation region to be displaced by growth of the bubbles; and a controller to control the displacement of movable member within a desired range. The heat-generating body and the discharge port are in a linearly communicating state so that the liquid is discharged from the discharge port with energy at the bubble generation, the controller being provided to face the bubble generation region of the liquid flow path, and a liquid flow path having the bubble generation region constituting a substantially closed space except the discharge port by substantial contact between the displaced movable member and the controller,
in which after commencement of disappearance of the bubbles formed by preceding liquid discharge, and under a state that the bubbles remain biased at the discharge port side in the bubble generation region and a portion where the bubbles do not exist is given rise to at the liquid chamber side of the bubble generation region, the liquid is caused to bubble by supplying the heat-generating body with driving energy for succeeding liquid discharge.
The present invention is not driven for the next discharge after the end of disappearance of a bubble formed at the time of the preceding liquid discharge, but is to execute discharge continuously at a timing by taking the balance between the succeeding bubble formation for discharge and the discharge, utilizing bubbles formed by the preceding liquid discharge, which is an epoch-making invention.
Paying attention to a movable member giving the above described efficient refilling characteristics, and in a liquid discharge head comprising the movable member. Taking as a clue that the bubble disappearance position is disposed at the discharge port side of the bubble generating region, the present invention has been realized by finding from the relationship between the bubble changes and the position of the meniscus that there is a timing for enabling discharge of liquid well prior to the end of bubble disappearance at the time of preceding liquid discharge.
That is, there is a timing such that the liquid discharge head including the movable member will present such a state that bubbles which have been formed due to the preceding liquid discharge but are on the verge of disappearance exist at the discharge port side of the bubble generation region and that bubbles do not exist at the position closer to the liquid chamber. In addition, in this timing, retreat of the meniscus has started but has not reached maximum. Further, since bubbles at the movable member side of the heat-generating body have disappeared, replenishment of the liquid has been substantially completed, and is in a sufficient refilling state. Accordingly, at this timing, the liquid discharge head is in an extremely advantageous state for executing the next discharge, and the driving energy for the next liquid discharge is supplied to the heat-generating body at this timing so that a consecutive liquid discharge can be executed properly. Execution of liquid consecutive discharge at this timing means consecutive execution of liquid is an extremely short interval compared with the case where the next liquid discharge is executed after completion of bubble disappearance as in the prior art.
In the method for discharging liquid of the present invention, the driving energy for liquid discharge continues under a state that a part of bubbles formed at the time of the preceding liquid discharge and which have remained at the downstream side is supplied to the heat-generating body. The liquid flow from the upstream side that is accompanied by disappearance of the bubbles which have remained at the downstream side affects the time of the liquid discharge for the second shot and onwards. This serves to improve energy efficiency of the liquid discharge for the succeeding liquid discharge. In addition, action of liquid flow from the upstream side can enlarge the volume of the discharged liquid droplet to be discharged at the time of liquid discharge for the second shot and onwards more than the volume of the discharged liquid droplet when the liquid discharge is executed from the normal state. In addition, the liquid flow from the upstream side can accelerate the flow of the liquid at the time of the succeeding liquid discharge, and can make the speed of the discharged liquid droplets at the time of liquid discharge for the second shot and onwards faster than the speed of the discharged liquid droplets at the time the liquid discharge has been executed from the normal state.
The liquid flow accompanied by disappearance of bubbles formed at the time of such a preceding liquid discharge is decelerated at the very end of disappearance as bubble disappearance progresses. Thus, before the bubbles having been formed at the time of the preceding liquid discharge completely disappear, foaming for the second shot and onwards commences so that the above described action of the liquid flow can be obtained effectively.
Thus, the volume of consecutive discharged liquid droplets being made larger and the speed thereof being made faster than those at the normal time will give advantages that they are convenient for multi-gradation recording.
As described above, according to the method for discharging liquid of the present invention, liquid discharge can be executed in a continuous fashion at an extremely short interval. Under these circumstances, at the time of the preceding liquid discharge, the part tailing backward of the discharged liquid droplet is separated to form the satellite, which can be arranged to be captured by the discharged liquid droplets at the succeeding liquid discharge. Thus, the succeeding discharged liquid droplets are made capable of capturing the satellite will give advantages that they are convenient for multi-gradation recording.
The discharged liquid droplets following the preceding discharged liquid droplets being made capable of capturing the satellite can be obtained for the first time by executing liquid discharge in a continuous fashion at an extremely short interval with the method for discharging liquid of the present invention. Under these circumstances, the method for discharging liquid of the present invention is a method for discharging liquid having a step to heat liquid filled in inside the liquid path with a heat-generating body to generate bubbles in the liquid and a step of discharge liquid with energy at the time when the bubbles from the discharge port that communicates with the liquid path are obtained to form discharged liquid droplets to be discharged and to discharge a plurality of discharged liquid droplets in a continuous fashion by repeating these steps a plurality of times, wherein the discharged liquid droplets discharged by the succeeding liquid discharge capture satellites while the satellites keep their shape as liquid pillars, and this discharged liquid droplet and the satellite are integrated. The satellite will become approximately spherical with surface tension during flying steps, but in the method for discharging liquid according to the present invention, as described above, capture by the discharged liquid droplets while keeping its liquid pillar shape immediately after the satellite is formed can be executed.
In addition, in the method for discharging liquid according to the present invention, at liquid discharge for the second time and onwards in consecutive discharges, a part of energy that was supplied at the preceding liquid discharge can be attributed to the succeeding liquid discharge effectively. Therefore at liquid discharge for the second time and onwards, energy less than the energy to be supplied to the heat-generating body at the liquid discharge for the first time is supplied to the heat-generating body so that the liquid discharge for the second time can be executed with droplet quantity and droplet velocity equal to or more than those at the time of liquid discharge for the first time.
Thus, the arrangement to make the energy to be supplied to the heat-generating body at the liquid discharge of the consecutive discharge for the second time and onwards smaller than that for the first time can be executed in particular by making a pulse width of a voltage pulse to be applied to the heat-generating body at the liquid discharge for the second time smaller than that for the first time.